1. Field of the Invention
The present invention relates to an electromagnetic wave concentrator, and more particularly to an electromagnetic wave concentrator suitable as a concentrate device for solar energy utilization or electromagnetic wave transceiver for communications, which is used for transmitting and receiving signals, and to a method for the manufacture thereof.
2. Description of the Related Art
The conventional electromagnetic wave concentrators have been manufactured by coating a lightweight thermoplastic resin with a high rigidity, such as CFRP (carbon fiber reinforced plastic) on an electromagnetic wave reflective surface typically obtained by molding a metallic thin film or net into the form of a paraboloid of revolution. The weight of such electromagnetic wave concentrators has been reduced by employing a structure in which a thermoplastic resin was coated on a metallic molded surface, but it was difficult to make a greater weight reduction further lowering the weight limit. When strict limitations are placed on the weight, such as in an electromagnetic wave concentrators for a space, a noticeable reduction in weight based on epoch-making technological improvement is required.
In order to reduce the weight further, a gas-inflatable electromagnetic wave concentrator has been considered in which a paraboloid of revolution is formed by subjecting an elastic film surface, e.g., a rubber surface to gas pressure. However, a paraboloid of revolution basically cannot be molded with sufficient precision by the gas inflation process. Furthermore, another transparent film has to be provided on the side of the reflective surface to seal the gas. In use, electromagnetic waves pass twice through the transparent film: once before reaching the reflective surface and once after the reflection from the reflective surface, and the loss therein is rather large. Furthermore, in the case of electromagnetic wave concentrators for space, if the holes are opened in the film due to collision of space debris with the electromagnetic wave concentrators, the gas starts to leak, making it impossible to maintain the gas pressure, and the form of a paraboloid of revolution cannot be maintained.
Accordingly, molding an electromagnetic wave concentrator from a single thin film, without gas inflation, can be considered. However, the following problem is associated with electromagnetic wave concentrators with a thin-film structure. It is precisely because of their thin-film structure that the rigidity of the reflective surface is very small and the shape of the reflective surface can easily collapse or turn inside out under the effect of vibrations or load. A thin-film electromagnetic wave concentrator can be fabricated by employing thermoplastic hardening of resins. However, the problem associated with such electromagnetic wave concentrators is that they have poor flexibility and can be easily cracked or deformed by impacts.
Further, there is also a method for increasing the rigidity of electromagnetic wave concentrators by coating the reflective film with a thermoplastic resin, as disclosed in Japanese Patent Applications Laid-open Nos. H5-305662 and H6-6127. However, with this method, the weight of electromagnetic wave concentrators is increased and when the concentrator has to be spread over a large surface area, in particular, as in space applications, it becomes a disadvantage from the standpoint of launching cost.
A method described in Japanese Patent Application Laid-open No. S62-168402, by which molding, mainly of metal materials, is conducted by inducing plastic deformation in a press by using a molding die, can be also considered, but the slip of metal atoms occurring during processing produces wrinkles on the reflective surface, and the decrease in reflection factor caused by the wrinkles is fatal, in particular, in the case of light concentrate mirrors.